Subject: RE: [Sip] Whats wrong with Supported.

From: "Gordon Ledgard" <[email-masked]>
Date: Mon, 7 Nov 2005 09:47:44 -0500

Yes, the Sup/Req/Acc/Acc-L headers have this problem with temporal
duration and scope. But they have another problem that digs deeper into
the biggest flaw of SIP, in my opinion:  SIP does a lousy job of
separating the functional layers of the network. Sip wants to be
your network connection (INVITE/OK/ACK), your discovery channel
(300 redirects and forking proxies), your router control protocol
(Route/RecordRoute), and your transport mechanism (SDP, etc), and your
session control manager(dialogs), all in one iddy-biddy packet.

Actually, the fact that it is all in one packet is not the problem.
That there is not a clearer definition of layered responsibilities is
the issue.

In fact SIP manages to do all this stuff amazingly well most of the
time,
and a hats off to everyone for that.

However, unless you can delineate these functionalities better, the
scope
of Sup/Req/Acc/Acc-L will remain fuzzy.

Gordon R. Ledgard
IPeria, Inc.

> 
> Paul Kyzivat wrote:
> 
> 
> > My other problem with Supported, Required, Accept, Accept-Language,
...
> > is that there is no clear definition of the scope over which this
> > declaration applies. Some possible interpretations are:
> > 1) just this message
> > 2) this transaction
> > 3) until the time of some action that the recipient is
> >    expected to take as a result of this message
> > 4) for the remainder of this dialog
> > 5) for the remainder of this dialog unless
> >   overridden later in the dialog
> > 6) for all messages with this UA
> > 7) for all messages with this UA unless
> >   overridden later

> .........
>
>   And Jonathan Rosenberg replied......
> 
> The difficulty as Paul has pointed out is that support for various
> extensions, headers, and methods is ultimately a property of a
> particular instance of software. However, a typical SIP URI, an in
> particular an AOR like sip:[email-masked], represents a user that can
> be reached at possibly many pieces of software. To make matters
messier,
> software can also be upgraded over time, so even if a UA routed to a
> particular instance, these properties arent truly static.
> 

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